JPS62248284A - System of locking frequency and phase for arrangement of lasers - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

Backlash of the invention 1 This invention relates to a Ray If control system,
In particular, it relates to techniques for determining the appropriate phase (at a common frequency for a two-dimensional array of radars featuring one frequency) at a uniform frequency other than each operating frequency different from the nominal frequency. The high power phased array implantation beam 1f has recently been developed; +17 i・
”Second Act

[It has become a research goal for researchers in the field of conics. One objective of this investigation is to obtain a coherent high power output beam for various applications. If it is desired to add individual laser powers to a single high-power beam into a coherent lens 1-14
The frequencies and relative phases of each beam must be locked together. Unfortunately, no method has yet been found to control the relative phase of a phased array IF. For example, using a (11L gallium oxide (GaAS)) radar with a nominal frequency of about 10"H7,
Typical frequency variations experienced between laps formed from similar processing equipment are on the order of a gigahertz, whereas Q
The aΔS rape can differ from the nominal frequency by several hundred V GHz. Often each laser itself chooses phases to make the threshold current (green) and often these phases are undesirable. For example, the Sudryf 7
- [Phase array diode tray] J' (P ha
sedΔrray [) t. de La5ers) J, Leb Focus (
1-asOrFocus) 100 pages (June 1984)
month) reference. Semiconductor lasers such as GaAs lasers are rapidly assuming an important role among all lasers. Due to their small size and inherent flexibility in design, semiconductor lasers have a wide range of a1! Useful for various applications. The problem of phase-locking outputs from multiple semiconductor radars is thus increasingly
, is becoming essential. When a large number of lasers are placed close enough together, an "evanescent" waveform is formed outside the boundaries of the individual beams,
It has been hypothesized that the result is energy coupling between adjacent lasers, thereby causing the various lasers to lock together in frequency and phase when they are close enough to each other. It has now been possible to create evanescent couplings for pi-linear arrays, i.e., in a two-dimensional R911, the frequencies and phases of the various radars must be locked together by some mechanism. There is still [ノC necessary C. SUMMARY OF THE INVENTION In addressing these problems in the prior art, the present invention establishes a common frequency and a common phase between an array of lasers characterized by a common nominal wavelength number and different individual operating frequencies. Provide new technology for The technology of this invention can be applied to a two-dimensional array of semiconductor rays I7''.
A portion of the r power is diverted to establish a common frequency and a common phase, and half of the diverted power varies according to the frequency deviation from the nominal. In an exemplary embodiment of the invention, waveguide v4T1 is positioned in the fF path of the beam emitted by the lasers in the array, and several optical gratings in each waveguide configuration are located in the waveguide. A portion of the beam propagating along the beam is deflected. The width of the waveguide structure and the length of the grating period are selected to establish the desired differentially guided propagation. In addition to deflecting a portion of the beam into the waveguide, each grating also deflects a portion of the previous guiding signal from the other gratings into the associated laser, thus enforcing a single operating frequency and phase. To establish this cross-coupling, the period of the grating is set to be substantially equal to λ/n, and the thickness of the waveguide core is small (r). Both are approximately λ/(4J) "Ko2 0.2
), where λ is the wavelength of the simplified t-do and n
, is the effective refractive index for the interconducting mode, and n and n are the respective refractive indices of the refraction for the σ cocoa support in the waveguide core J3. may be provided by a series of physical asperities on the surface of the waveguide, as a photogravity grating, or by some other beam deflection structure.The effective depth of the grating is determined by the desired depth. Directly proportional to the deviation between the nominal frequency and the individual radar operating frequency 'C' of the beam power deflected by the grating (il is the frequency deviation to be overcome and phase T7: I!+ The circumference fil for each grating can be set at a constant level to yield a single intermediate mode, or it can be set at a constant level to yield a single intermediate mode, or it can be set at a constant level along the grating if several different allegories are desired. [changed C
Good too. One of the main advantages of this invention is that it achieves cross-coupling between the various seams in a two-dimensional array, rather than being restricted to a linear array, and thus achieves frequency and phase locking. That is to say. In one embodiment, this two-dimensional bamboo is achieved with semiconductor lasers by positioning the lasers 1 minute closer to each other in one direction, and evanescent coupling between adjacent lasers provides a common operating frequency and phase for adjacent lasers. established in that direction, the waveguide grating is oriented to establish a common operating frequency and phase between the rapes in the other direction. Alternatively, a plurality of gratings may be installed in the waveguide in alignment with each beam, with the grating for each beam oriented to deflect a portion of the beam in two desired directions. be done. For deflection of the laser in an x-y array, a pair of gratings may be provided aligned with each array along opposing surfaces of the waveguide structure. The invention is particularly suitable for use with semiconductor radars. Because of this El, the waveguide core is made of a transparent substrate - [
The right-hand side includes the @ membrane generated in the second phase, and the entire structure is ray+p.
The array itself may be monolithically integrated. Additional features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, which refers to the accompanying drawings. The principle of operation of the J cornerstone of this invention is illustrated in FIG. 1, in which the Radhe 2 array is constructed using, for example, a gallium arsenide (gallium arsenide) beam which produces a beam with a nominal wavelength of approximately 8500 Å. GaAs)'F) It has been shown that it can be a four-body laser. The emitted laser beam 4 passes through a substray 1-8 which is substantially transparent to the laser beam.
and a waveguide structure 6 consisting of a waveguide core 10 held and supported by ribs. Various techniques can be used to form the waveguide core on one substrate, such as thin film production. Good references to explain thin film production techniques are Oni 7 Riff D3 and Ir.
-("y'arlv & YQh) Optical Waves in C
rystals) J, pp. 405-503 (John Wilcy & Sons)
& 5ons) 1984i1:). GaAs
In a semiconductor laser, the substrate may be a transparent glass and the core may include a thin film of another glass with a higher index of refraction. For this purpose, metals may be diffused into the core glass to achieve a "flint" glass with a higher refractive index. The core index of refraction is designated here as n2, while the core index of refraction is designated as n. The waveguide structure is also characterized in that light guidance is usually not completely confined within the core, but rather influenced by the lip rate on one side of the core and the air in contact with the other side of the core. i [effectiveness] that takes into account the pretext
It may be characterized by a refractive index n. The "effective" refractive index, n, is a commercial combination of the refractive index for the core, nub [rate, and air] and is usually n.
Less than 2 but greater than n. Waveguide core 10 includes a series of optical gratings 12 on one surface formed in alignment with respective laser beams 4 . Then: the waveguide structure is grating 1 as described in T.I.
2 is shaped so that a portion of each laser beam is propagated along the waveguide core 10. A large portion of each laser beam is transmitted through and out of the waveguide structure without substantial deflection, as shown by arrow 14, while a smaller portion of the laser beam is transmitted through the waveguide structure on both the left and right sides, as shown by arrow 16. deflected towards. Typically, the deflection portion is a few percent of the total beam. The guiding part of each beam passes through the grating for the other beams, so! ! l! ! A portion of the guided beam is deflected by the second grating into the laser for the grating, i.e. the current shown by the downward pointing arrow 18.Successive portions of the guided beam arise from each rake. is fractionated into a 1.L laser as the beam continues to propagate along the waveguide. H. A cross-coupling is established between the various lasers so that some of their beams are deflected to other lasers in the array. It has been found that, despite the individual deviations from the common frequency, it is possible to efficiently drive various radars for a common frequency J3.J: and t6. The discovery of standards for the just-described cross-coupling !1.structures''--contains a key part of this invention. , the conduction coefficient β of the waveguide L-de, and the period of the various gratings. An enlarged view of the waveguide core at one location I5 of the grating 12 is illustrated in FIG. is depicted as a series of 1'F sinusoidal asperities on the upper surface of the core with a period of 1. The thickness of the waveguide core is given by As it propagates down the core, it is deflected and leaves the boundary of the waveguide core.The guided beam is deflected and leaves the grating 12 at an angle to the incoming laser beam 4. The deflected portion 18 of the aS beam directed toward A is indicated by a dashed line.The deflected beam 18 is adjacent to the incoming laser beam 4 and is directed toward C.
However, in reality, it is substantially coaxial with the incoming beam. The relationships that establish the necessary conditions for cross-coupling and uniform See 11 frequency and phase are as follows. △-2π/β-△/n+1)
-λ /
) modes, each of which is characterized by its unique β. Equation 2) is TEM, . Represents the core thickness at cutoff for the mode. This is the HA limit rL allowed for the core, and if additional propagation modes are desired, the core thickness can be increased correspondingly. The depth of the grating ensures that adequate power is deflected from the sea 1F beam into the waveguide to establish sufficient cross-coupling to set the laser frequency and phase of J. but should not be substantially greater than the minimum value to avoid any unnecessary loss of power.The required grating depth is As the deviation between and the actual laser operating frequency increases, it increases with a corresponding increase in the deflected power peak.A typical grating depth is approximately 10% to 20% of the core thickness l. If propagation in more than one t-mode is desired, the perimeter 111 of the grating can be varied somewhat within each grating, and therefore different parts of the same grating can be The configuration of a waveguide structure with a period corresponding to the propagation constant of the desired mode.The configuration of a waveguide structure with dimensions that change in response to the desired mode is called ``ping''.A myriad of techniques are available. are used to form an optical grating 12. The gratings may consist of physical asperities in the waveguide core, as illustrated in FIG. 2, or they may be formed as "holographic" gratings. In a later attempt, two C-Ir beams are folded into an angle at the waveguide surface to form an interference pattern. This pattern is then folded into an optical structure that may not have physical asperities. While a series of uneven ridges and grooves are used to define the grid, their actual sides may be triangular, square, or other than ridges. Taking on various forms like objects II
Ru. The asperities can be formed by a number of different methods, such as electron beam or ion beam implantation, photolithography, or the use of etchants. Relative changes in refractive index on the order of a few percent have been reported as a result of ion implantation. For example, Townpinto (Townsend)
Author, 5PrE Newsletter, New Optical Materials (New Ooti
calMaterials) page 88 (Geneva, Switzerland, April 1983). A resolution of about 500 angstroms and a reasonably sized area! High-precision conbuque-controlled ion beams are also available at Microbeam Inn = 1-Boleyat (Mlc) in Nico Berry Park, California.
It has been made commercially available by companies such as Robeam, Inc.). The selection of specific ionic species and their energies determine the strength of the lattice. The embodiment of the invention illustrated in FIGS. 1 and 2 utilizes a sea 1F beam oriented perpendicular to the waveguide core. The other relative angle between the laser beam and the waveguide structure is also (
Each grating has a limited acceptance angle within which a portion of the incident sea 1r beam is deflected along the waveguide core and propagated at .
Therefore, C51 is used, while the remainder of the beam is transmitted out of the waveguide. The acceptance angle for a particular grating generally depends on the periodicity and sides of the grating's asperities. With a 90 degree orientation between the beam and the grating, the grating generally exhibits only one order of diffraction along the four-wave core. 60
For very small angles of incidence, such as degrees, there are two or more diffraction orders of -F, one of which is along the waveguide. The exception to this is 1
A "blazed" grating, it has only a single order of diffraction when the angle of incidence of the laser beam is less than 90 degrees. As noted, the strength of cross-coupling between various lasers will be determined by the depth of modulation in the grating. This corresponds to a frequency band within which all frequencies and phases of the laser can be locked together at a given strength of cross-coupling. In other words, the frequencies and phases of these lasers will be locked together if the frequency difference between them is within the bandwidth. By using the invention to combine the outputs of a number of V, conductor lasers with a frequency and phase common to lasers of much higher power. A two-dimensional semiconductor laser 11 using the present invention to co-cook the frequencies and phases of various lasers.
The arrangement is illustrated in FIG. ray IJ” 20 is x-y
Arranged in an array. . Adjacent lasers are spaced relatively far apart along the X-axis and direct their respective laser 17' beams toward a coupling prism 22 disposed between each pair of lasers in the X-direction. , this form of structure is proposed by Liau [Surface-emitting C with low threshold current and high efficiency]
a In AS P/In P laser (Surrac
Ellittin (l Ca I n As P/
I 11PLaser With I-ow Th
reshold Current and 1lio
h EHiciency) Applied Physics Letters (△DDIIQd P hys;as
+-ctters), vol. 46, p. 115 (1985)
, 8 prisms are grating 2 which deflects the incident beam in the X direction.
4 is used to deflect their incident laser beams into a four-wave core 23 configured as previously described. 5° ray to cross-couple each of the lasers along the axis!/' Gt C1 to emit the beam only in the X direction
The adjacent laser in the Y direction is fabricated very close to U and is 1rJ. If the lasers were brought together sufficiently close together in the Y direction (J), they would establish a common frequency and phase in the Y direction by "evanescent" wave coupling. An "evanescent" wave existing outside the range of , thereby combining with an adjacent beam in physical proximity f1k of -1 minutes, causes the beams to cross together in frequency and phase, as is known in the art. [1] Evanescent coupling, as known in the art, operates only in linear arrangements, and its use to date has been limited to such arrangements. The -y arrangement is shown to lock adjacent laser frequencies and phases in one direction via evanescent coupling, and to lock the lasers frequency and phase in the other direction, as indicated by the dashed lines in Figure 3. The waveguide and grating structures are set up as shown in Figure 3. Since the divine laser I7' is now tied together in both directions, all of the lasers in the entire array have essentially the same common frequency and The system illustrated in FIG. It may also be possible to incorporate a waveguide structure into the substrate layer of a two-dimensional laser array to create a single monolithic integrated structure that is compact and robust. Another form of the invention is shown in Fig. 4, where the lattice is a unidirectional lattice and a multidirectional lattice.
Rather than using spring tip coupling, a waveguide is used to optically couple a two-dimensional array of bidirectional Helleys 1j. In this embodiment, several stages of beams 12G are arranged in a two-dimensional array (only one dimension is shown in FIG. 4 for simplicity) and a waveguide structure 28 equivalent to the waveguide shown in FIG. suspended above the laser array. The waveguide structure 2B includes a transparent substrate 1 to 30 and a core 32 with relative refractive indices as previously described. The upper surface of core 32 has a plurality of spaced gratings 34 aligned with respective beams for the various lasers. The gratings 34 are formed to deflect and propagate portions of their respective rays IJ'' beams along the waveguide core in the Xh direction. A second set of gratings 36 again has one grating aligned with each laser beam, causing cross-coupling between lasers on the same X-axis to establish frequency and phase.C, waveguide core 32 The gratings 36 are oriented at a 90 degree angle to the gratings 34 and deflect a portion of their respective Radhe beams along the waveguide core 32 in the Y direction. This is due to the cross-coupling between the radars along each Y axis and the resulting 1
．． (Waveguide propagation along the As the lasers along the Y-axis exhibit a common frequency and phase, the result is that all of the lasers throughout the two-dimensional array have a common frequency and phase. The above explanation is based on the fact that the laser is an x-y matrix C11L! It is assumed that the Of course, other laser array formats are possible, and in this case the orientation of the various gratings is adapted accordingly from the rigid ('h Dimension Ray 1
Various embodiments of systems and methods for establishing a common frequency and phase for an array are thus shown and described. Numerous variations and alternative embodiments are described in Section 1. A person who is proficient in this may be able to think of
It is intended that the invention be limited only as to the scope of the appended claims.

[Brief explanation of drawings]

FIG. 1 is a laser array and cross-coupled waveguide structure drawn in accordance with the present invention to establish a common frequency and threat phase for the various lasers in the array. FIG. 2 is an enlarged elevational view illustrating a grating used to deflect portions of the Lede beam into and out of the waveguide. FIG. 3 is a cutaway projection of a laser array and waveguide structure illustrating the achievement of Thief cross-coupling in one dimension by evanescent coupling and in the pond dimension by means of a waveguide. FIG. 4 is a schematic diagram of a Rade array and waveguide structure in which a pair of gratings is installed in the waveguide for each laser beam to deflect the beam in two vl directions. In the figure 33, 2 is the radar, 4 is the laser beam, and 6) 1
10 is the waveguide core, 12 is the optical grating, 14 and 16 are the sea 1F beams, 18 is the polarized beam, 20 is the rape, 22 is the coupling prism, and 23 is the waveguide. A core or waveguide structure, 241 and a grating, 26 a laser, 28 a waveguide structure, 30 a transparent substrate, 32 a waveguide core, 34 and 36 a grating, and 38 and 40 arrows. Patent applicant: Rockwell International Corporation

Claims (21)

[Claims] (1) A frequency and phase locking system for an array of lasers emitting beams characterized by a uniform nominal frequency other than individual operating frequencies that are offset from the nominal frequency emitted by the lasers in the array. a waveguide structure positioned in the path of the beam; and a plurality of optical gratings formed in the waveguide structure;
Each grating in the plurality is aligned with the beam from one of the lasers in the array, and the thickness of the waveguide structure and the period of the grating are
a portion of each beam is selected to be deflected to propagate along the waveguide and cross-couple with other lasers in the array;
A system thereby establishing a common operating frequency and phase for an array of lasers. (2) the lasers are positioned sufficiently close to each other in a first direction of the array that the evanescent coupling establishes a common operating frequency and phase for adjacent lasers in the first direction; and 5. The system of claim 1, wherein the lasers are arranged in a two-dimensional array, oriented to establish a common operating frequency and phase between the lasers in two directions. (3) the plurality of gratings are oriented to establish a common operating frequency and phase in a first direction of the array, and further formed into a waveguide structure and oriented in a second direction of the array. 2, each grating in the second plurality being aligned with a beam from one of the lasers in the array, and forming a thickness of the waveguide structure and a second plurality of optical gratings; The period of the grating is selected such that a portion of each beam propagates along the waveguide in the second direction and is deflected to intersect other lasers in the array in the second direction, thereby 6. The system of claim 1, wherein the lasers are arranged in a two-dimensional array, establishing a common operating frequency and phase between the lasers in a second direction of the array. (4) The system of claim 3, wherein gratings for two directions are positioned on opposite surfaces of the waveguide structure. 5. The system of claim 1, wherein the grating further comprises a series of asperities on the surface of the waveguide structure. 6. The system of claim 1, wherein the grating further comprises a holographic grating formed in a waveguide structure. 7. The system of claim 1, wherein the period of each grating is varied along the grating to make the grating responsive to a plurality of different waveguide modes. (8) establishing a common operating frequency and phase for the cross-coupled laser with a substantially laser-transparent waveguide structure substrate overlaid with a waveguide core layer in the path of the beam emitted by the laser; A plurality of optical fibers formed in the core layer and aligned with each laser beam to deflect a portion of the beam to propagate along the waveguide core and cross-couple with other lasers in the array. a grating, the period of the grating is substantially equal to λ/n_1, and the thickness of the core is at least approximately λ/[4√(n_2^2−n_
3^2)], where λ is the wavelength of the bulking mode, n_1 is the effective refractive index for the bulking mode, and
and where n_2 and n_3 are the refractive indices of the waveguide core and substrate, respectively, for a laser array emitting a beam characterized by a uniform nominal frequency, excluding individual operating frequencies that deviate from the nominal frequency. and phase locking system. 9. The system of claim 8, wherein the effective depth of the optical grating is established in direct proportion to the deviation between the nominal frequency and the individual laser operating frequency. (10) The system of claim 8, wherein the waveguide core layer comprises a thin film disposed on the substrate layer. 11. The system of claim 8, wherein the waveguide structure is monolithically integrated with the Rade array. (12) the lasers are positioned sufficiently close to each other in one direction to establish a common operating frequency and phase for adjacent lasers in that direction via evanescent coupling between adjacent lasers; 9. The system of claim 8, wherein the lasers are arranged in a two-dimensional array, wherein the waveguide gratings are oriented in different directions to establish a common operating frequency and phase between the lasers. (13) the plurality of gratings are oriented along one axis of the matrix to establish a common operating frequency and phase between the lasers, and are further aligned with their respective laser beams and lasers in another direction of the array; 9. A second plurality of optical gratings in a waveguide structure oriented to establish a common operating frequency and phase therebetween, wherein the lasers are arranged in a two-dimensional array. The system described. 14. The system of claim 13, wherein gratings for two axes of the laser array are positioned along opposite surfaces of the waveguide structure. 15. The system of claim 8, wherein the grating includes a series of asperities on the surface of the waveguide structure. 16. The system of claim 8, wherein the grating comprises a holographic grating formed in a waveguide structure. 17. The system of claim 8, wherein the period of each grating is varied along the grating to make the grating responsive to a plurality of different bulking modes. (18) deflecting and cross-coupling a portion of the beam emitted by each of the lasers in the array with other lasers in the array; and transmitting the undeflected portion of the beam along respective predetermined paths. and establishing a common operating frequency and phase for an array of lasers characterized by a uniform nominal frequency excluding individual operating frequencies that deviate from the nominal frequency. (19) the beam is directed to each grating in a waveguide;
Portions of the beam are deflected for propagation along the waveguide by their respective gratings, and the deflected beam portions for each laser are further deflected by deflection in the gratings for those lasers in the array. 19. The method of claim 18 for cross-coupling with other lasers. (20) Each laser is cross-coupled to less than all of the remaining lasers in the array and further to other lasers in the array to establish a common operating frequency and phase with said other lasers by evanescent coupling. Claim 1 comprising the step of positioning each laser in sufficient proximity.
The method described in Section 9. (21) Portions of the beam emitted by each of the lasers in the array are deflected in multiple directions along the waveguide, thereby establishing cross-coupling between each laser and the two-dimensional array of other lasers. 20. The method of claim 19, wherein: